In a wireless communication system supporting a High Speed Downlink Pack Access (HSDPA) service, a Hybrid Automatic Repeat Request (HARQ) scheme is used as a link adaptation technique. In a HSDPA system, a terminal may receive Downlink (DL) data from a base station through a High-Speed Downlink Shared Channel (HS-DSCH), and transmit uplink data through a High-Speed Dedicated Physical Control Channel (HS-DPCCH).
The terminal may measure a received common pilot channel to help the base station to determine a channel state and transmit a Channel Quality Indicator (CQI) reflecting the measurement result through the HS-DPCCH. The base station may transmit packet data to which Adaptive Modulation and Coding (AMC) is applied. A modulation scheme and a channel coding rate of a channel may vary with a channel change indicated by the CQI to improve the throughput of the channel. Further, the terminal may feed back successful or failing reception of the transmitted packet data using an Acknowledgement (ACK) or a Negative Acknowledgement (NACK) through the HS-DPCC to notify retransmission or non-retransmission. In the HSDPA system, 2 ms (corresponding to 3 slots) may be defined as one subframe and a Transmission Time Interval (TTI), and in the HS-DPCCH, HARQ ACK or NACK information may be fed back to the base station in the first slot.
When the ACK/NACK is fed back in the HS-DPCCH, a transmit power (hereinafter, referred to as a HS-DPCCH transmit power or an ACK/NACK feedback transmit power) may be determined based on values signaled by the base station based on DPCCH closed loop power control using combined Transmit Power Control (TPC). If the DPCCH power control is performed by combining TPC included in the active set, a serving cell requests power may increase. If a combining result of active sets is power decrease, the request of the serving cell may be difficult to be accepted. When the transmit power of the HS-DPCCH is determined based on a value determined by the base station, the terminal may not change an Uplink (UL) transmit power until being instructed by the base station even when the terminal senses rapid deterioration of the channel state. As a result, it is difficult to reflect the channel state to the UL transmit power in real time. If the transmit power of the HS-DPCCH does not increase when the wireless channel state is deteriorated, the ACK/NACK feedback transmission error rate may increase, and thus the terminal may fail to receive desired data. As a result, the rapid retransmission and error recovery capabilities, which are known advantages of HARQ, may be deteriorated, and thus data throughput may be degraded. Therefore, properly adjusting the transmit power of the HS-DPCCH according to an UL channel state may be desired.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as related art with regard to the present disclosure.